In hot rolling, a state of phase transformation changes in accordance with temperature history of a steel plate and, accordingly, mechanical properties such as strength of a final product vary. Thus, it is extremely important to manage a temperature of each part of a steel plate. PTL 1 below discloses an apparatus which calculates a temperature distribution of a cross section perpendicular to a longitudinal direction of a steel plate in hot rolling. The apparatus described in PTL 1 annularly divides a steel plate in spatial increments into a plurality of elements from an outer periphery to a center of a cross section of the steel plate and calculates a predicted temperature of each divided element by a difference method.
With a steel plate in hot rolling, a temperature of an edge part is likely to be lower than a temperature of a central part in a plate-width direction. In some cases, an edge heater is provided on a rolling line as equipment for correcting low temperature of an edge part. An edge heater heats only the edge part of a steel plate with induction heating.
PTL 2 below discloses a method of calculating an amount of lost heat from an edge part by air cooling, a coolant, and roll contact between an edge heater and a rolling mill and correcting an amount of applied heat by the edge heater so that the edge part reaches a target temperature on an entry side of the rolling mill.